The invention relates to a Hadamard spectrometer which enables the detection of a number of polyatomic gases or liquids using, for example, infrared absorption. Such devices are utilized, in particular, for emission control, workplace inspection, and environmental monitoring.
With respect to prior art related to the invention, reference is made to a spectrophotometer disclosed in U.S. Pat. No. 5,257,086 which enables a mathematical evaluation of detected spectral data and, hence, a spectral analysis under use of the Hadamard transformation. The spectrophotometer described therein is provided with a radiation source array, which is typically an essential unit for spectrometers. The individual radiation sources of the radiation source array provide different wavelengths which can be controlled in accordance with the Hadamard method. The spectrophotometer includes an imaging diffraction grating with a detector arranged behind a slit for detecting spectral signals, and electronic units which ensure a very fast spectral analysis of a sample to be examined. The essential advantage resulting from the Hadamard transformation is a considerable improvement of the signal-to-noise ratio. A disadvantage of the arrangement described in U.S. Pat. No. 5,257,086 is that at first LEDs have to be available as radiation sources which correspond to the frequency spectrum to be examined, and this at present limits the arrangement to a wavelength spectrum of from 250 nm to about 2.5 .mu.m. Another significant disadvantage of this device is that considerable expenditures have to be spent in order to stabilize the intensities of the individual LEDs in order to obtain spectra which can be analyzed quantitatively.
Furthermore, spectrometers are known, namely the monolithic miniature spectrometer designated MMS 1 manufactured by Carl Zeiss, Business Field for Special Engineering, Sales Department for Optical Components, D-73446 Oberkochen, Germany, in which diode rows are employed as detecting elements. In this case, it is required to image a spectral line onto at least three adjacent detector elements. Only the three measurement signals obtained permit a precise detection of the wavelength. Hence, the resolution power of such spectrometers with respect to a wavelength interval is limited by the number of the detector elements employed and their mutual distance.